The decrease in breast feeding among infants in the U.S. from 1940 to 1975 has been reflected in Native American populations in a shorter period of time. This study described changes in breast feeding among the Pima Indians living on a reservation in Arizona and compared the health effects of breast and bottle fed infants over the past 20 years. The availability of centralized health records at the Sacaton Hospital of the Indian Health Service and the relative lack of mobility of the population made this an excellent source for a study of this issue of current national concern.